1. Field of the Invention
The present invention relates generally to an implantable hearing prosthesis and, more particularly, to an implantable microphone for an implantable hearing prosthesis.
2. Related Art
Medical devices having one or more implantable components, generally referred to as implantable medical devices, have provided a wide range of therapeutic benefits to patients over recent decades. One type of implantable medical devices, implantable hearing prostheses, treat the hearing loss of a prosthesis recipient are one particular type of implantable medical devices that are widely used today.
Hearing loss, which may be due to many different causes, is generally of two types, conductive and sensorineural. In some cases, a person suffers from hearing loss of both types. Conductive hearing loss occurs when the normal mechanical pathway that sound travels to reach the cochlea is impeded, for example, by damage to the ossicles. Individuals suffering from conductive hearing loss typically have some form of residual hearing because the hair cells in the cochlea are undamaged. As a result, individuals suffering from conductive hearing loss typically receive an implantable hearing prosthesis, such as an acoustic hearing aid, middle ear implant, etc., that generates mechanical motion of the cochlea fluid.
In many people who are profoundly deaf, however, the reason for their deafness is sensorineural hearing loss. Sensorineural hearing loss occurs when there is damage to the inner ear, or to the nerve pathways from the inner ear to the brain. As such, those suffering from some forms of sensorineural hearing loss are thus unable to derive suitable benefit from hearing prostheses that generate mechanical motion of the cochlea fluid. Such individuals may benefit from implantable hearing prostheses that deliver electrical stimulation to nerve cells of the recipient's auditory system. As used herein, a recipient's auditory system includes all sensory system components used to perceive a sound signal, such as hearing sensation receptors, neural pathways, including the auditory nerve and spiral ganglion, and the regions of the brain used to sense sounds. Electrically-stimulating hearing prostheses include, but are not limited to, auditory brain stimulators and cochlear implants.
Cochlear implants are often proposed when the sensorineural hearing loss is due to the absence or destruction of the cochlear hair cells which transduce acoustic signals into nerve impulses. Cochlear implants generally include a stimulating assembly implanted in the cochlea to deliver electrical stimulation signals to the auditory nerve cells, thereby bypassing absent or defective hair cells. The electrodes of the stimulating assembly differentially activate auditory neurons that normally encode differential pitches of sound.
Auditory brain stimulators are often proposed to treat a smaller number of individuals with bilateral degeneration of the auditory nerve. For such recipients, an auditory brain stimulator provides stimulation of the cochlear nucleus in the brainstem.
Totally or fully implantable forms of the above and other implantable hearing prostheses have been developed to treat a recipient's conductive, sensorineural and/or combination hearing loss. As used herein, a totally implantable hearing prosthesis refers to a device in which all of the components of the device are implanted subcutaneously; that is there are no external components. One exemplary totally implantable cochlear implant is described in greater detail in U.S. Pat. No. 7,346,397, which is hereby incorporated by reference herein.
Unlike conventional hearing prostheses in which microphones are positioned external to the recipient, a totally implantable hearing prosthesis includes a subcutaneously-implanted microphone. An implanted microphone may be sensitive to airborne sound, referred to herein as air-conducted sound, as well as sound conducted to the microphone via the bones, tissue, etc. of the recipient's head, referred to herein as body-noise.